When a tractor-trailer or other truck is backed-up to a loading dock of a factory, warehouse or the like, it is now a general safety practice to place a wedge-shaped stop block or chock on the pavement, against the fronts of at least one left wheel and a least one right wheel. This is done so that while the trailer or other cargo container/support of the truck is being loaded or unloaded, the truck cannot roll forwards, or be driven away.
In the years before the use of wheel blocks became such a general safety practice, it occasionally happened that a truck driver upon returning to his or her vehicle and mistakenly concluding that loading/unloading operations were completed and that all loading/unloading personnel were clear of the cargo container, got in his or her cab and drove-off. At that time any person still engaged in loading/unloading the cargo container of the truck was likely to be injured, especially if they were at the time operating a fork-lift truck within the cargo container.
Fortunately, the widespread adoption and common use of wheel blocks has eliminated much of the safety problem.
However, there remains the possibility that someone would remove the wheel blocks from in front of the wheels of a truck before loading/unloading operations have been completed, and the truck roll forward or be driven off, with there then being almost the same likelihood for damage and injury as there would have been had no wheel blocks been used at all.
In the experience of the present inventor, when the wheel blocks are removed prematurely, it is usually done without care or authorization; for instance, the truck driver may mistakenly believe loading/unloading has been completed and become over-anxious to be on his or her way. Or the driver or a person assisting with the arrival of a newly arrived truck may "borrow" the blocks from under another truck at the loading dock, in the mistaken belief that the other truck has no further need for them.
In other cases, especially where a truck is left at a loading dock of a plant which is unattended or only lightly guarded overnight or over a weekend, thieves or vandals seeking to carry away anything accessible that is of conceivable value may steal the wheel blocks simply because they are so portable.
It has previously occurred to others that a way for preventing premature removal of wheel blocks from blocking relation to truck wheels is to establish some sort of tethering relationship between the blocks while they are in use, and the truck wheels or with some adjacent portions of the truck, and then provide a locking means for preventing that tethering relationship from being terminated without authorization. An example of a prior art solution is found in the U.S. Pat. No. 4,399,893, of Switzer, issued Aug. 23, 1983.
However, prior art proposals for solving the unauthorized, premature removal of chocks problem have tended to be mechanically complex and, particularly, not susceptible to adaptation to existing chocks, i.e. by retrofitting.